1 saw 1.1 \documentclass{chowto}
2
3 \title{Drift Chamber Gas System Operation}
4 \howtotype{expert} % ``expert'', ``user'', ``reference''
5 %\experiment{Name of experiment} % Optional
6 \author{H. Fenker}
7 \category{general} % Subject area of this document
8 % Allowed choices are
9 %
10 % hms HMS detectors and other HMS stuff (eg rotation)
11 % sos SOS detectors and other SOS stuff i(eg doors)
12 % magnet SOS/HMS or other magnet systems
13 % beamline Beamline instrumentation
14 % daq Data Acuisition and Analysis
15 % electronics
16 % target
17 % general All other subjects
18
19 %\maintainer{Name of person maintaining document} % Optional
20 \date{March 3, 2003}
21
22 saw 1.1
23 \begin{document}
24 \providecommand{\degg}{\ensuremath{^{\circ}\ }}
25
26 \begin{abstract}
27 This document provides detailed setup information for the drift chamber gas mixing
28 system, as well as the correct procedure for refilling the alcohol supply and changing
29 gas bottles. This information is intended for use by {\bf gas system experts only.}
30 For day-to-day shift worker instructions, refer to the corresponding {\it user} howto
31 document.
32 \end{abstract}
33
34 \section{Overview}
35
36
37 The drift chamber gas is composed of 50\% Argon and 50\% Ethane (by volume),
38 bubbled through isopropanol at 1\degg C. The mixing system that produces this
39 gas is housed in the gas shed. The bottles supplying the gas to the mixing
40 system are attached to two two-bottle manifolds outside the gas shed, within
41 the fenced-in gas bottle yard.
42
43 saw 1.1 \section{Settings for Normal Operation}
44
45 Refer to the gas system flow diagram, Fig. \ref{fig:gas_mixer_diagram}
46 \begin{figure}
47 \psfig{figure=drift_gas_system-HallCGasMixlvl1.eps,width=6in,bbllx=12,bblly=12,bburx=750,bbury=590}
48 \caption{Diagram of Hall~C Gas Mixing System\label{fig:gas_mixer_diagram}}
49 \end{figure}
50
51
52 For normal operation, with the alcohol systems in use, the valves
53 should be set as follows:
54
55 {\bf For The HMS:}
56
57 Open - 3, 4, 11, 14; Closed - 12, 13, 17, 18, 19, 20.
58
59 The nominal flows set in the mass flow controller are:
60 \begin{itemize}
61 \item Channel 3 (Argon): 0.3~slpm (standard liters per minute)
62 \item Channel 4 (Ethane): 0.3~slpm
63 \end{itemize}
64 saw 1.1
65
66 Unless the gas \#3 Mass flow control valve is installed, valve \#6 should
67 always be closed.
68
69 {\bf For the SOS:}
70
71 Open - 1, 2, 7, 10; Closed - 8, 9, 15, 16, 19, 21.
72 \begin{itemize}
73 \item Channel 1 (Argon): 0.15~slpm
74 \item Channel 2 (Ethane): 0.15~slpm
75 \end{itemize}
76
77
78 Unless the gas \#3 Mass flow control valve is installed, valve \#5 should
79 always be closed.
80
81 \section{Operating the Mass Flow Controller.}
82
83 The gas flow is controlled by a MKS 647 controller and mass flow
84 control valves. The 647 is menu driven from a CRT in the front panel and
85 saw 1.1 with a keypad with cursor controls. The 647 features a non-volatile memory
86 so settings are retained even if the unit is unpowered. The initial menu
87 upon startup is the Command Menu. For normal operation use either the User
88 Display menu (Command menu item \#1) or the Extended Display menu (Command
89 menu item \#2). The User Display menu shows actual flow in each channel and
90 the total flow in all channels. The Extended Display menu shows actual
91 flow, flow set point, units, valve full scale range, gas calibration
92 factor, whether that channel is enabled, and whether each channel is
93 operating in master, slave, or independent mode.
94
95 \subsection{To set flow rates:}
96
97 The flow rate set points are adjusted from the Extended Display
98 menu. There are two methods to change valve flow rate set point. If you
99 want to enter a specific value you must first turn off the flow in that
100 channel or all of the channels. Using the cursor keys move the cursor to
101 the desired channel. Enter the desired flow rate.
102
103 The flow rate set point can be changed with gas flowing using the
104 cursor keys. In the Extended Display mode move the cursor to the desired
105 channel using the left/right cursor keys. The set point can then be
106 saw 1.1 adjusted up or down using the cursor up/down keys.
107
108 \subsection{To turn gas flow on or off:}
109
110 The gas flow can be turned on or off while in any menu. When any
111 of the mass flow valves are open the green LED labeled ``GAS ON" on the 647
112 is lit. When none of the gas flow valves are open the red ``STAND BY" LED
113 will be flashing. In the Extended Display menu the bottom line displays on
114 or off, by channel, to show which mass flow valves are enabled. The green
115 LED must be lit and an ``ON" must be displayed in the bottom row of the
116 Extended Display menu for gas to be flowing in a particular channel.
117
118 {\bf Turning the gas on or off is done in two steps which can be done in
119 either order.}
120 Each channel must be enabled by pressing ``ON" and then
121 that channel number. The command input must be enabled by pressing ``ON"
122 and then ``ALL" from the keypad. This allows a single channel or all of the
123 enabled channels to be turned on or off at once. Both steps must be
124 performed initially, but thereafter only one of the steps need be performed
125 to cycle the gas flow on or off.
126
127 saw 1.1 To turn gas off in a single channel press ``OFF" and then the
128 desired channel. If you want to close all the valves simultaneously, press
129 the ``OFF" key and then the ``ALL/0" key. To turn gas back on you must
130 reverse whichever sequence you used to stop the gas flow. For example if
131 you turned the gas off by pressing ``OFF" and then the channel number, it
132 must be turned back on by pressing ``on" and then the channel number. If
133 you turn off all the channels by pressing ``OFF" , ``ALL" you must turn it
134 back on by pressing ``ON" , ``ALL."
135
136 \section{To Change a Gas Bottle}
137
138 Handling and connecting bottles of compressed gas requires special knowledge.
139 The high pressure gas stored in the cylinders (bottles) constitutes significant
140 stored energy. Mishandling of a gas bottle can pose a lethal hazard! Refer to
141 the JLab EH\&S Manual \cite{bi:jlabehs} for safe handling practices. If you do not already know
142 how to safely manipulate compressed gas hardware, have a knowledgeable
143 person train you.
144 \section{To by-pass the alcohol system:}
145
146 For the HMS:
147 Open valves 12 \& 13, then close valves 11 \& 14, in that order!
148 saw 1.1
149 For the SOS:
150 Open valves 8 \& 9, then close valves 7 \& 10, in that order!
151
152 \section{The Alcohol Bubblers}
153
154 To reduce the rate of aging of the wire chambers, the operating gas contains
155 a small quantity of alcohol vapor. The vapor is added by bubbling the argon/ethane
156 mixture through liquid alcohol. The temperature of the alcohol controls the
157 alcohol vapor pressure, which determines the
158 amount of vapor added to the gas. The alcohol content also affects the
159 electron dirft velocity in the wire chambers, so it must be held
160 approximately constant.
161
162 \subsection{To refill the alcohol bubblers:}
163
164 The alcohol bubbler system features a refill system that allows
165 filling directly from the bottle, minimizing exposure of the alcohol to air
166 and reducing the possibility of a spill.
167 {\bf The reservoirs should be refilled
168 before they become empty to maintain a head of liquid over the float valve
169 saw 1.1 which will prevent air from entering the system.}
170 In the back of the gas
171 system rack is a holder for gallon sized alcohol bottles and a cap with dip
172 tube. Place a new bottle in the bottle holder and replace the cap with the
173 cap with dip tube.
174
175 \subsection{Step-by-Step Instructions for Refilling the SOS Alcohol Bubbler}
176 \em{These steps must be individually completed in the order listed!}\\
177 Refer to Fig.~\ref{fig:gas_mixer_diagram}.
178 \begin{enumerate}
179 \item{If needed, install a full bottle of alcohol in the back of the gas racks as mentioned in the preceeding paragraph.}
180 \item{{\em Open valves 8,9. Close valves 7,10} to Put the SOS alcohol bubbler in BYPASS.}
181 \item{{\em Close valve 16} to isolate the warm reservoir gas from the bubbler.}
182 \item{{\em Open valve 15} to bleed off the warm reservoir gas pressure.}
183 \item{{\em Open valve 19} to pressurize the alcohol bottle.}
184 \item{{\em Open valve 21} to flow alcohol into the warm reservoir.}
185 \item{When the alcohol level in the sight-glass is within 2cm of the top, stop
186 the flow of alcohol: {\em Close valve 21.}}
187 \item{{\em Close valve 19.}}
188 \item{{\em Open valve 16.}}
189 \item{{\em Close valve 15.}}
190 saw 1.1 \item{{\em Open Valves 7 and 10. Close Valves 8 and 9.}}
191 \item{Record what you did in both the gas logbook and the electronic logbook.}
192 \end{enumerate}
193
194 \subsection{Step-by-Step Instructions for Refilling the HMS Alcohol Bubbler}
195 \em{These steps must be individually completed in the order listed!}\\
196 Refer to Fig.~\ref{fig:gas_mixer_diagram}.
197 \begin{enumerate}
198 \item{If needed, install a full bottle of alcohol in the back of the gas racks as mentioned in the preceeding paragraph.}
199 \item{ {\em Open valves 12,13. Close valves 11,14} to Put the HMS alcohol bubbler in BYPASS.}
200 \item{{\em Close valve 18} to isolate the warm reservoir gas from the bubbler.}
201 \item{{\em Open valve 17} to bleed off the warm reservoir gas pressure.}
202 \item{{\em Open valve 19} to pressurize the alcohol bottle.}
203 \item{{\em Open valve 20} to flow alcohol into the warm reservoir.}
204 \item{When the alcohol level in the sight-glass is within 2cm of the top, stop
205 the flow of alcohol: {\em Close valve 20.}}
206 \item{{\em Close valve 19.}}
207 \item{{\em Open valve 18.}}
208 \item{{\em Close valve 17.}}
209 \item{{\em Open Valves 11 and 14. Close Valves 12 and 13.}}
210 \item{Record what you did in both the gas logbook and the electronic logbook.}
211 saw 1.1 \end{enumerate}
212
213 \subsection {Alcohol Temperature Control}
214
215 To keep the alcohol temperature (and thus the vapor pressure) constant,
216 the alcohol bubblers are housed in refrigerators which are controlled by
217 electronic temperature regulators having 1~C\degg sensitivity. Both
218 controllers are located on a shelf in the left rack of the gas mixing
219 system. Normally, the actual temperature in each refrigerator is
220 indicated on the front panel of the controller. Both controllers should
221 be set to maintain a temperature of 1\degg C.
222
223 \section{Gas Filters Maintenance}
224
225 There are gas filters on the argon and ethane supply lines just inside
226 the gas shed. These filters should be replaced on a regular schedule.
227 See Bill Vulcan for details.
228
229 \section{Secure Pressure Regulators}
230
231 The gas mixing system is protected from failure or mis-setting of the
232 saw 1.1 primary pressure regulators (the ones mounted on the manifolds on the
233 exterior of the gas shed -- near the bottles) by {\it hidden} regulators
234 mounted just inside the gas shed. It is these regulators which actually
235 set the maximum supply pressure to the mixing valves. These regulators
236 should {\em never} be adjusted by other than a gas system expert! The
237 nominal secondary pressure supplied by both the argon and ethane
238 secure regulators is 15 psig.
239
240
241 \section{Related {\it Howtos}}
242 \begin{itemize}
243 \item MKS 647 Mass Flow Controller Howto \cite{howto:MKS_controller_TM}
244 \item Flammable Gas Detector System \cite{howto:flam_gas_detector}
245 \item Gas System Interlock Panel \cite{howto:gas_interlock_panel}
246 \item Base Equipment Shift Checklist Items \cite{howto:base_equip_checklist}
247 \end{itemize}
248
249 \end{document}
250
251 % Revision history:
252 % 1st draft by Howard Fenker 27FEB03 -- taken from existing ops manual.
253 saw 1.1 % $Log$
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